When seeking information about potential internal problems, Taylor said, a horse’s collateral sulci (the grooves located adjacent to the frog) can be very telling. The sulci run parallel to and remain a fixed distance from the bottom of the coffin bone in the front half of the hoof and the collateral cartilages in the rear half of the hoof. The sulci should be relatively linear and shouldn’t undulate in depth. She explained that unlike many other hoof structures, the depth and contour of the collateral sulci aren’t typically altered by hoof care efforts.
In a healthy foot, the distance between the ground and the collateral sulci, where they converge at the apex of the frog, is 10 to 20 millimeters, Taylor said. The coffin bone’s concave solar surface (located on the bottom of the bone, just above the sole of the foot) sits about 10 to 11 millimeters above this point.
There could be problems when the collateral sulci develop a stair-step or undulating shape and become significantly deeper in the heel, Taylor said: This shape, often found on horses with long toes and “underrun” heels, is likely indicative of poor heel development. She recommended veterinarians perform radiographs on hooves with this conformation to evaluate the coffin bone’s position; the palmar/plantar processes of these coffin bones might be dangerously close to the ground, she said. Some veterinarians hypothesize that the negative palmar/plantar angle is associated with lameness in not only the foot but also proximal (higher) portions of the limb.
“This conformation in hind feet may be associated with pain in the hocks, suspensory ligaments, gluteal and lumbar regions,” Taylor said.